The actions of the neurotransmitter 5-hydroxytryptamine (5-HT) are mediated through a number of receptor families termed 5-HT.sub.1, 5-HT.sub.2, 5-HT.sub.3, 5-HT.sub.4, 5-HT.sub.5, 5-HT.sub.6, and 5-HT.sub.7 (see D. Hoyer et al., Pharmacol. Rev., 1994, 46, 157-204). Although the functions of the 5-HT.sub.5, 5-HT.sub.6 and 5-HT.sub.7 receptors are less well understood than the functions of the other 5-HT receptors, it is generally accepted that compounds which selectively interfere with 5-HT-mediated signal transduction are important novel drug targets. In particular, 5-HT.sub.6 selective ligands have been identified as potentially useful in the treatment of certain CNS disorders such as Parkinson's disease, Huntingdon's disease, anxiety, depression, manic depression, psychosis, epilepsy, obsessive compulsive disorders, migraine, Alzheimers disease (enhancement of cognitive memory), sleep disorders, feeding disorders such as anorexia and bulimia, panic attacks, withdrawal from drug abuse such as cocaine, ethanol, nicotine and benzodiazepines, schizophrenia, and also disorders associated with spinal trauma and/or head injury such as hydrocephalus. Such compounds are also expected to be of use in the treatment of certain GI (gastrointestinal) disorders such is IBS (Irritable Bowel Syndrome). (See WO98/27058, WO98/27081, Drug News Perspectives, 1997, 10, 214 and A. J. Sleight et al., Serotonin ID Research Alert, 1997, 2(3), 115-8).
A wide variety of 5-HT analogues incorporating an indole nucleus have been prepared and tested for pharmacological effects, but hitherto none has been shown to be a selective ligand for 5-HT.sub.6 receptors. WO-A-98/27058 and WO-A-98/27081 disclose, respectively, sulphonamides and carboxamides which are 5-HT.sub.6 receptor antagonists, but none of the compounds disclosed comprises an indole or indoline nucleus. Similarly, certain benzenesulphonamides of non-indole nature are disclosed as selective 5-HT.sub.6 antagonists in EP-A-815861 and in Br.J.Pharinacol., 1998, 124, 556-562.
Many analogues of 5-HT are known, comprising a 1-acyl- or 1-arylsulphonyl-3-(2-aminoethyl) indole nucleus (see, for example, U.S. Pat. Nos. 3,481,953 and 3,489,429). Fused-ring analogues, such as trans-4-dimethylamino-1-(4-methylbenzenesulphonyl)-1,3,4,5-tetrahydrobenz[ cd]indol-5-ol, are also known (J.Chem.Soc., Perkin Trans. I, 1973, 438-42). Analogues comprising a 4-(2-N,N-dialkylaminoethyl)indole nucleus, unsubstituted in the 1-position, have been shown to be dopamine agonists (Eur. J. Med. Chem., 1991, 26, 473-5; J. Med. Chem., 1984, 27, 386-9). However, the 1-substituted derivatives disclosed herein are believed to be novel.